OS is RHEL 6.2.

I appear to be having an issue with SELinux. I've disabled it in /etc/sysconfig/selinux, however, when my host starts the command sestatus show that I'm in permissive mode.

Searches in Stack Exchange bring me to this U&L Q&A: How to permamently disable SELinux?. That question mentions a scenario that sounds similar to mine.

Which prompted me to have the following questions:

  1. what does net.ipv4.tcp_syncookies=1 (=0) means?
  2. Is it safe to turn to this to 0?

NOTE: My original problem is related to automount/nfs.

Sometimes when a distant Filesystem is neither mounted nor unmounted, we have to restart autofs. I don't know if this is happening under heavy traffic or if this issue is related to the net.ipv4.tcp_syncookies problem above or not.

So I'm trying to get a better understanding of net.ipv4.tcp_syncookies so that I can ascertain whether this is related to my autofs problem or nott.

  • What does the SELinux bit have to do with your 2 questions? As it stands your Q is a bit confusing. If you can clean it up we can reopen it. – slm Sep 22 '14 at 12:57
  • @slm Searches in Stack Exchange bring me this: unix.stackexchange.com/questions/30342/…, on this page disabling selinux is related to net.ipv4.tcp_syncookies, I was just asking for precision. Sorry to have been unclear. – Archemar Sep 22 '14 at 13:03
  • OK, I think I see what you're asking now. I've edited the Q further and reopened. Thanks! – slm Sep 22 '14 at 13:08


Helps in preventing SYN flood attack on the system. A value of 0 will disable it.From security point of view, it is ideal to keep it on i.e. set value to 1. However, its pretty safe to turn it off.

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